Last week I showed you Static Addition and Subtraction using the bead frames. This week, the kids are demonstrating using exchanges for Dynamic addition and subtraction. Dynamic addition involves carrying, and dynamic subtraction uses the borrowing method. What you’ll see the boys doing is using the exchange method, since one bead on the 10 bar equals 10 beads on the units bar, for example, they can be exchanged for each other, like 10 one dollar bills for one 10 dollar bill. Here is Iain showing his dynamic addition problem that he’s working on:
Pretty straightforward. But Eryk had a slightly trickier subtraction problem, where he had to make an exchange with tens and hundreds, but didn’t have any hundreds to make the exchange with. That forced him to make two exchanges before he could proceed. Check it out:
And he got it! I let my kids check their answers with a calculator when I don’t have time to sit with them and check their work. I figure that they will be using the calculators for quick math sooner rather than later,
Two Math weeks in a row! I promise something different next week.